Oxalate selectively activates p38 mitogen-activated protein kinase and c-Jun N-terminal kinase signal transduction pathways in renal epithelial cells

Sulfated Laminarin Polysaccharides Reduce the Adhesion of Nano-COM Crystals to Renal Epithelial Cells by Inhibiting Oxidative and Endoplasmic Reticulum Stress

Purpose: Adhesion between calcium oxalate crystals and renal tubular epithelial cells is a vital cause of renal stone formation; however, the drugs that inhibit crystal adhesion and the mechanism of inhibition have yet to be explored. Methods: The cell injury model was constructed using nano-COM crystals, and changes in oxidative stress levels, endoplasmic reticulum (ER) stress levels, downstream p38 MAPK protein expression, apoptosis, adhesion protein osteopontin expression, and cell-crystal adhesion were examined in the presence of Laminarin polysaccharide (DLP) and sulfated DLP (SDLP) under protected and unprotected conditions. Results: Both DLP and SDLP inhibited nano-COM damage to human kidney proximal tubular epithelial cell (HK-2), increased cell viability, decreased ROS levels, reduced the opening of mitochondrial membrane permeability transition pore, markedly reduced ER Ca2+ ion concentration and adhesion molecule OPN expression, down-regulated the expression of ER stress signature proteins including CHOP, Caspase 12, and p38 MAPK, and decreased the apoptosis rate of cells. SDLP has a better protective effect on cells than DLP. Conclusions: SDLP protects HK-2 cells from nano-COM crystal-induced apoptosis by reducing oxidative and ER stress levels and their downstream factors, thereby reducing crystal-cell adhesion interactions and the risks of kidney stone formation.

Identification of the pivotal role of SPP1 in kidney stone disease based on multiple bioinformatics analysis

Background

Kidney stone disease (KSD) is a multifactorial disease involving both environmental and genetic factors, whose pathogenesis remains unclear. This study aims to explore the hub genes related to stone formation that could serve as potential therapeutic targets.

Methods

Based on the GSE73680 dataset with 62 samples, differentially expressed genes (DEGs) between Randall’s plaque (RP) tissues and normal tissues were screened and weighted gene co-expression network analysis (WGCNA) was applied to identify key modules associated with KSD. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis were performed to explore the biological functions. The protein–protein interaction (PPI) network was constructed to identify hub genes. Meanwhile, CIBERSORT and ssGSEA analysis were used to estimate the infiltration level of the immune cells. The correlations between hub genes and immune infiltration levels were also investigated. Finally, the top hub gene was selected for further GSEA analysis.

Results

A total of 116 DEGs, including 73 up-regulated and 43 down-regulated genes, were screened in the dataset. The red module was identified as the key module correlated with KSD. 53 genes were obtained for functional enrichment analysis by taking the intersection of DEGs and genes in the red module. GO analysis showed that these genes were mainly involved in extracellular matrix organization (ECM) and extracellular structure organization, and others. KEGG analysis revealed that the pathways of aldosterone-regulated sodium reabsorption, cell adhesion molecules, arachidonic acid (AA) metabolism, and ECM-receptor interaction were enriched. Through PPI network construction, 30 hub genes were identified. CIBERSORT analysis revealed a significantly increased proportion of M0 macrophages, while ssGSEA revealed no significant differences. Among these hub genes, SPP1, LCN2, MMP7, MUC1, SCNN1A, CLU, SLP1, LAMC2, and CYSLTR2 were positively correlated with macrophages infiltration. GSEA analysis found that positive regulation of JNK activity was enriched in RP tissues with high SPP1 expression, while negative regulation of IL-1β production was enriched in the low-SPP1 subgroup.

Conclusions

There are 30 hub genes associated with KSD, among which SPP1 is the top hub gene with the most extensive links with other hub genes. SPP1 might play a pivotal role in the pathogenesis of KSD, which is expected to become a potential therapeutic target, while its interaction with macrophages in KSD needs further investigation.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12920-022-01157-4.

P38 MAPK signaling pathway mediates COM crystal-induced crystal adhesion change in rat renal tubular epithelial cells

The objective of the study is to clarify the mechanism of p38 mitogen-activated protein kinase (p38 MAPK) signaling pathway in the change of crystal adhesion in rat renal tubular epithelial cells (NRK-52E) induced by calcium oxalate monohydrate (COM) crystals. NRK-52E cells were divided into COM crystal-treated group and control group according to whether the cell culture medium contains different concentrations of COM crystals. The concentrations of lactate dehydrogenase in the both group medium were determined after being cultured for 24 h. Protein and RNA were extracted from both cell groups after being cultured at different time points. SB239063, an inhibitor of the activation of p38 MAPK, was pretreated for 2 h before incubation with COM crystals. Western blotting and RT-qPCR were performed to confirm the expression levels of relative genes. All the experimental results were summarized and analyzed by SPSS 20.0 statistical analysis software. COM crystals (146 µg/cm²) could induce the expression levels of NLRP3, caspase-1 and interleukin-1β (IL-1β) significantly increased in NRK-52E cells. Compared with the control group cells, the transcription and translation levels of p38 MAPK-related molecule (such as p-p38) and adhesion molecules (such as osteopontin, hyaluronic acid and CD44) were significantly increased in COM crystal-treated cells and can be inhibited by SB239063 and NLRP3 gene silencing. This study demonstrated that the p38 MAPK signaling pathway mediated the COM crystal-induced crystal adhesion change in NRK-52E cells and required the involvement of NLRP3 inflammasome.

Losartan Ameliorates Calcium Oxalate-Induced Elevation of Stone-Related Proteins in Renal Tubular Cells by Inhibiting NADPH Oxidase and Oxidative Stress

Calcium oxalate (CaOx) is the most common type of urinary stone. Increase of ROS and NADPH oxidase gives rise to inflammation and injury of renal tubular cells, which promotes CaOx stone formation. Recent studies have revealed that the renin-angiotensin system might play a role in kidney crystallization and ROS production. Here, we investigated the involvement of Ang II/AT1R and losartan in CaOx stone formation. NRK-52E cells were incubated with CaOx crystals, and glyoxylic acid-induced hyperoxaluric rats were treated with losartan. Oxidative stress statuses were evaluated by detection of ROS, oxidative products (8-OHdG and MDA), and antioxidant enzymes (SOD and CAT). Expression of NADPH oxidase subunits (Nox2 and Nox4), NF-κB pathway subunits (p50 and p65), and stone-related proteins such as OPN, CD44, and MCP-1 was determined by Western blotting. The results revealed upregulation of Ang II/AT1R by CaOx treatment. CaOx-induced ROS and stone-related protein upregulation were mediated by the Ang II/AT1R signaling pathway. Losartan ameliorated renal tubular cell expression of stone-related proteins and renal crystallization by inhibiting NADPH oxidase and oxidative stress. We conclude that losartan might be a promising preventive and therapeutic candidate for hyperoxaluria nephrolithiasis.

Kidney Stone Disease: An Update on Current Concepts

Kidney stone disease is a crystal concretion formed usually within the kidneys. It is an increasing urological disorder of human health, affecting about 12% of the world population. It has been associated with an increased risk of end-stage renal failure. The etiology of kidney stone is multifactorial. The most common type of kidney stone is calcium oxalate formed at Randall's plaque on the renal papillary surfaces. The mechanism of stone formation is a complex process which results from several physicochemical events including supersaturation, nucleation, growth, aggregation, and retention of urinary stone constituents within tubular cells. These steps are modulated by an imbalance between factors that promote or inhibit urinary crystallization. It is also noted that cellular injury promotes retention of particles on renal papillary surfaces. The exposure of renal epithelial cells to oxalate causes a signaling cascade which leads to apoptosis by p38 mitogen-activated protein kinase pathways. Currently, there is no satisfactory drug to cure and/or prevent kidney stone recurrences. Thus, further understanding of the pathophysiology of kidney stone formation is a research area to manage urolithiasis using new drugs. Therefore, this review has intended to provide a compiled up-to-date information on kidney stone etiology, pathogenesis, and prevention approaches.

Calcium Oxalate Induces Renal Injury through Calcium-Sensing Receptor

Objective. To investigate whether calcium-sensing receptor (CaSR) plays a role in calcium-oxalate-induced renal injury. Materials and Methods. HK-2 cells and rats were treated with calcium oxalate (CaOx) crystals with or without pretreatment with the CaSR-specific agonist gadolinium chloride (GdCl₃) or the CaSR-specific antagonist NPS2390. Changes in oxidative stress (OS) in HK-2 cells and rat kidneys were assessed. In addition, CaSR, extracellular signal-regulated protein kinase (ERK), c-Jun N-terminal protein kinase (JNK), and p38 expression was determined. Further, crystal adhesion assay was performed in vitro, and the serum urea and creatinine levels and crystal deposition in the kidneys were also examined. Results. CaOx increased CaSR, ERK, JNK, and p38 protein expression and OS in vitro and in vivo. These deleterious changes were further enhanced upon pretreatment with the CaSR agonist GdCl₃ but were attenuated by the specific CaSR inhibitor NPS2390 compared with CaOx treatment alone. Pretreatment with GdCl₃ further increased in vitro and in vivo crystal adhesion and renal hypofunction. In contrast, pretreatment with NPS2390 decreased in vitro and in vivo crystal adhesion and renal hypofunction. Conclusions. CaOx-induced renal injury is related to CaSR-mediated OS and increased mitogen-activated protein kinase (MAPK) signaling, which subsequently leads to CaOx crystal adhesion.

Oxalate induces breast cancer

BACKGROUND

Microcalcifications can be the early and only presenting sign of breast cancer. One shared characteristic of breast cancer is the appearance of mammographic mammary microcalcifications that can routinely be used to detect breast cancer in its initial stages, which is of key importance due to the possibility that early detection allows the application of more conservative therapies for a better patient outcome. The mechanism by which mammary microcalcifications are formed is still largely unknown but breast cancers presenting microcalcifications are more often associated with a poorer prognosis.

METHODS

We combined Capillary Electrochromatography, histology, and gene expression (qRT-PCR) to analyze patient-matched normal breast tissue vs. breast tumor. Potential carcinogenicity of oxalate was tested by its inoculation into mice. All data were subjected to statistical analysis.

RESULTS

To study the biological significance of oxalates within the breast tumor microenvironment, we measured oxalate concentration in both human breast tumor tissues and adjoining non-pathological breast tissues. We found that all tested breast tumor tissues contain a higher concentration of oxalates than their counterpart non-pathological breast tissue. Moreover, it was established that oxalate induces proliferation of breast cells and stimulates the expression of a pro-tumorigenic gene c-fos. Furthermore, oxalate generates highly malignant and undifferentiated tumors when it was injected into the mammary fatpad in female mice, but not when injected into their back, indicating that oxalate does not induce cancer formation in all types of tissues. Moreover, neither human kidney-epithelial cells nor mouse fibroblast cells proliferate when are treated with oxalate.

CONCLUSIONS

We found that the chronic exposure of breast epithelial cells to oxalate promotes the transformation of breast cells from normal to tumor cells, inducing the expression of a proto-oncogen as c-fos and proliferation in breast cancer cells. Furthermore, oxalate has a carcinogenic effect when injected into the mammary fatpad in mice, generating highly malignant and undifferentiated tumors with the characteristics of fibrosarcomas of the breast. As oxalates seem to promote these differences, it is expected that a significant reduction in the incidence of breast cancer tumors could be reached if it were possible to control oxalate production or its carcinogenic activity.

Inhibition to DRP1 translocation can mitigate p38 MAPK-signaling pathway activation in GMC induced by hyperglycemia

Diabetic nephropathy (DN) is a serious complication of diabetes with a poorly defined etiology and limited treatment options. Early intervention is a key to preventing the progression of DN. Dynamin-related protein 1 (DRP1) regulates mitochondrial morphology by promoting its fission and is involved in the pathogenesis of numerous diseases. Furthermore, DRP1 is also closely associated with the development of diabetes, but its functional role in DN remains unknown. This study investigated the effect of DRP1 on early stage of DN. DRP1 expression has increased significantly in glomerular mesangial cell (GMC), which is cultivated in high glucose (HG). Ultra-microstructural changes of nephrons, expression of collagen IV and phosph-p38, ROS production, and mitochondrial function were evaluated and, at the same time, were compared with glomerular mesangial cell (GMC) cultured in normal-glucose (NG), mannitol, and a medium with mitochondrial division inhibitor 1 (Midivi-1). Endogenous DRP1 expression increased in DN. Compared to the control groups ofNG and mannitol, overexpression of DRP1 destroyed pathological changes typical of the GMC, like accumulation of extracellular matrix, and an increase in mitochondria division. In addition, Overexpression of DRP1 promoted the activation of p38, the accumulation of ROS, mitochondrial dysfunction, and the synthesis of collagen IV, and all these changes are suppressed by Midivi-1. This study demonstrates that DRP1 overexpression can accelerate pathological changes in the GMC cultured in HG. Further studies are needed to clarify the underlying mechanism of this destructive function.

Analysis of altered microRNA expression profiles in proximal renal tubular cells in response to calcium oxalate monohydrate crystal adhesion: implications for kidney stone disease

BACKGROUND

Calcium oxalate monohydrate (COM) is the major crystalline component in kidney stones and its adhesion to renal tubular cells leads to tubular injury. However, COM-induced toxic effects in renal tubular cells remain ambiguous. MicroRNAs (miRNAs) play an important role in gene regulation at the posttranscriptional levels.

OBJECTIVE

The present study aimed to assess the potential changes in microRNAs of proximal renal tubular cells in response to the adhesion of calcium oxalate monohydrate (COM) crystals.

METHODOLOGY

Lactate dehydrogenase (LDH) activity and DAPI staining were used to measure the toxic effects of HK-2 cells exposed to COM crystals. MicroRNA microarray and mRNA microarray were applied to evaluate the expression of HK-2 cells exposed to COM crystals. Quantitative real-time PCR (qRT-PCR) technology was used to validate the microarray results. Target prediction, Gene Ontology (GO) analysis and pathway analysis were applied to predict the potential roles of microRNAs in biological processes.

PRINCIPAL FINDINGS

Our study showed that COM crystals significantly altered the global expression profile of miRNAs in vitro. After 24 h treatment with a dose (1 mmol/L), 25 miRNAs were differentially expressed with a more than 1.5-fold change, of these miRNAs, 16 were up-regulated and 9 were down-regulated. A majority of these differentially expressed miRNAs were associated with cell death, mitochondrion and metabolic process. Target prediction and GO analysis suggested that these differentially expressed miRNAs potentially targeted many genes which were related to apoptosis, regulation of metabolic process, intracellular signaling cascade, insulin signaling pathway and type 2 diabetes.

CONCLUSION

Our study provides new insights into the role of miRNAs in the pathogenesis associated with nephrolithiasis.

Oxalate upregulates expression of IL-2Rβ and activates IL-2R signaling in HK-2 cells, a line of human renal epithelial cells

The role of inflammation in oxalate-induced nephrolithiasis is debated. Our gene expression study indicated an increase in interleukin-2 receptor β (IL-2Rβ) mRNA in response to oxalate (Koul S, Khandrika L, Meacham RB, Koul HK. PLoS ONE 7: e43886, 2012). Herein, we evaluated IL-2Rβ expression and its downstream signaling pathway in HK-2 cells in an effort to understand the mechanisms of oxalate nephrotoxicity. HK-2 cells were exposed to oxalate for various time points in the presence or absence of SB203580, a specific p38 MAPK inhibitor. Gene expression data were analyzed by Ingenuity Pathway Analysis software. mRNA expression was quantitated via real-time PCR, and changes in protein expression/kinase activation were analyzed by Western blotting. Exposure of HK-2 cells to oxalate resulted in increased transcription of IL-2Rβ mRNA and increased protein levels. Oxalate treatment also activated the IL-2Rβ signaling pathway (JAK1/STAT5 phosphorylation). Moreover, the increase in IL-2Rβ protein was dependent upon p38 MAPK activity. These results suggest that oxalate-induced activation of the IL-2Rβ pathway may lead to a plethora of cellular changes, the most common of which is the induction of inflammation. These results suggest a central role for the p38 MAPK pathway in mediating the effects of oxalate in renal cells, and additional studies may provide the key to unlocking novel biochemical targets in stone disease.

An update on oxidative stress-mediated organ pathophysiology

Exposure to environmental pollutants and drugs can result in pathophysiological situations in the body. Research in this area is essential as the knowledge on cellular survival and death would help in designing effective therapeutic strategies that are needed for the maintenance of the normal physiological functions of the body. In this regard, naturally occurring bio-molecules can be considered as potential therapeutic targets as they are normally available in commonly consumed foodstuffs and are thought to have minimum side effects. This review article describes the detailed mechanisms of oxidative stress-mediated organ pathophysiology and the ultimate fate of the cells either to survive or to undergo necrotic or apoptotic death. The mechanisms underlying the beneficial role of a number of naturally occurring bioactive molecules in oxidative stress-mediated organ pathophysiology have also been included in the review. The review provides useful information about the recent progress in understanding the mechanism(s) of various types of organ pathophysiology, the complex cross-talk between these pathways, as well as their modulation in stressed conditions. Additionally, it suggests possible therapeutic applications of a number of naturally occurring bioactive molecules in conditions involving oxidative stress.

Arjunolic acid: a new multifunctional therapeutic promise of alternative medicine

IMPORTANCE OF THE FIELD

In recent years, a number of studies describing the effective therapeutic strategies of medicinal plants and their active constituents in traditional medicine have been reported. Indeed, tremendous demand for the development and implementation of these plant derived biomolecules in complementary and alternative medicine is increasing and appear to be promising candidates for pharmaceutical industrial research. These new molecules, especially those from natural resources, are considered as potential therapeutic targets, because they are derived from commonly consumed foodstuff and are considered to be safe for humans.

AREAS COVERED IN THIS REVIEW

This review highlights the beneficial role of arjunolic acid, a naturally occurring chiral triterpenoid saponin, in various organ pathophysiology and the underlying mechanism of its protective action. Studies on the biochemistry and pharmacology suggest the potential use of arjunolic acid as a novel promising therapeutic strategy.

WHAT THE READERS WILL GAIN

The multifunctional therapeutic application of arjunolic acid has already been documented by its various biological functions including antioxidant, anti-fungal, anti-bacterial, anticholinesterase, antitumor, antiasthmatic, wound healing and insect growth inhibitor activities. The scientific basis behind its therapeutic application as a cardioprotective agent in traditional medicine is justified by its ability to prevent myocardial necrosis and apoptosis, platelet aggregation, coagulation and lowering of blood pressure, heart rate, as well as cholesterol levels. Its antioxidant property coupled with metal chelating property (by its two hydroxyl groups) protects different organs from metal and drug-induced organ pathophysiology. Arjunolic acid also plays a beneficial role in the pathogenesis of diabetes and its associated complications. The mechanism of cytoprotection of arjunolic acid, at least in part, results from the detoxification of reactive oxygen species (ROS) produced in the respective pathophysiology. In addition to its other biological functions, it also possesses vibrant insecticidal properties and it has the potential to be used as a structural molecular framework for the design of molecular receptors in the general area of supramolecular chemistry and nanochemistry. Esters of arjunolic acid function as organogelators which has wide application in designing thermochromic switches and sensor devices. Arjunolic acid derived crown ether is an attractive candidate for the design of molecular receptors, biomimetics and supramolecular systems capable of performing some biological functions.

HOME MESSAGE

This review would provide useful information about the recent progress of natural product research in the domain of clinical science. This review also aims to untie the multifunctional therapeutic application of arjunolic acid, a nanometer-long naturally occurring chiral triterpenoid biomolecule.

p38 MAPK mediates calcium oxalate crystal-induced tight junction disruption in distal renal tubular epithelial cells

We examined whether p38 MAPK plays role in calcium oxalate monohydrate (COM) crystal-induced tight junction disruption. Polarized MDCK cells were pretreated with or without 20 μM SB239063 (p38 MAPK inhibitor) for 2-h, and then incubated with 100 μg/ml COM crystals for up to 48-h. Western blotting showed increased level of phospho-p38, not total p38, in COM-treated cells, whereas SB239063 pretreatment successfully maintained phospho-p38 at its basal level. COM crystals also caused decreased levels of two tight junction proteins, zonula occludens-1 (ZO-1) and occludin. Immunofluorescence study revealed disruption of tight junction, redistribution, and dissociation of ZO-1 and occludin. Moreover, transepithelial resistance (TER) showed defective barrier function, whereas Western blotting for Na⁺/K⁺-ATPase-α1 revealed defective fence function of tight junction in COM-treated cells. All these expression and functional defects were successfully prevented by SB239063 pretreatment. These findings indicate that COM crystals cause tight junction disruption in distal renal tubular epithelial cells through p38 MAPK activation.

Genome wide analysis of differentially expressed genes in HK-2 cells, a line of human kidney epithelial cells in response to oxalate

Nephrolithiasis is a multi-factorial disease which, in the majority of cases, involves the renal deposition of calcium oxalate. Oxalate is a metabolic end product excreted primarily by the kidney. Previous studies have shown that elevated levels of oxalate are detrimental to the renal epithelial cells; however, oxalate renal epithelial cell interactions are not completely understood. In this study, we utilized an unbiased approach of gene expression profiling using Affymetrix HG_U133_plus2 gene chips to understand the global gene expression changes in human renal epithelial cells [HK-2] after exposure to oxalate. We analyzed the expression of 47,000 transcripts and variants, including 38,500 well characterized human genes, in the HK2 cells after 4 hours and 24 hours of oxalate exposure. Gene expression was compared among replicates as per the Affymetrix statistical program. Gene expression among various groups was compared using various analytical tools, and differentially expressed genes were classified according to the Gene Ontology Functional Category. The results from this study show that oxalate exposure induces significant expression changes in many genes. We show for the first time that oxalate exposure induces as well as shuts off genes differentially. We found 750 up-regulated and 2276 down-regulated genes which have not been reported before. Our results also show that renal cells exposed to oxalate results in the regulation of genes that are associated with specific molecular function, biological processes, and other cellular components. In addition we have identified a set of 20 genes that is differentially regulated by oxalate irrespective of duration of exposure and may be useful in monitoring oxalate nephrotoxicity. Taken together our studies profile global gene expression changes and provide a unique insight into oxalate renal cell interactions and oxalate nephrotoxicity.

Kidney injury molecule-1 is up-regulated in renal epithelial cells in response to oxalate in vitro and in renal tissues in response to hyperoxaluria in vivo

Oxalate is a metabolic end product excreted by the kidney. Mild increases in urinary oxalate are most commonly associated with Nephrolithiasis. Chronically high levels of urinary oxalate, as seen in patients with primary hyperoxaluria, are driving factor for recurrent renal stones, and ultimately lead to renal failure, calcification of soft tissue and premature death. In previous studies others and we have demonstrated that high levels of oxalate promote injury of renal epithelial cells. However, methods to monitor oxalate induced renal injury are limited. In the present study we evaluated changes in expression of Kidney Injury Molecule-1 (KIM-1) in response to oxalate in human renal cells (HK2 cells) in culture and in renal tissue and urine samples in hyperoxaluric animals which mimic in vitro and in vivo models of hyper-oxaluria. Results presented, herein demonstrate that oxalate exposure resulted in increased expression of KIM-1 m RNA as well as protein in HK2 cells. These effects were rapid and concentration dependent. Using in vivo models of hyperoxaluria we observed elevated expression of KIM-1 in renal tissues of hyperoxaluric rats as compared to normal controls. The increase in KIM-1 was both at protein and mRNA level, suggesting transcriptional activation of KIM-1 in response to oxalate exposure. Interestingly, in addition to increased KIM-1 expression, we observed increased levels of the ectodomain of KIM-1 in urine collected from hyperoxaluric rats. To the best of our knowledge our studies are the first direct demonstration of regulation of KIM-1 in response to oxalate exposure in renal epithelial cells in vitro and in vivo. Our results suggest that detection of KIM-1 over-expression and measurement of the ectodomain of KIM-1 in urine may hold promise as a marker to monitor oxalate nephrotoxicity in hyperoxaluria.

Cyclooxygenase 2 and prostaglandin E2 regulate the attachment of calcium oxalate crystals to renal epithelial cells

OBJECTIVE

To determine the roles of endogenous cyclooxygenase 2 and prostaglandin E(2) in crystal-cell binding, which is considered to be an important step in the development of intratubular nephrocalcinosis.

METHODS

An expression plasmid for human cyclooxygenase 2 was introduced into Madin-Darby canine kidney cells using the lipofection method. Cyclooxygenase activity was measured using thin-layer chromatography, and the prostaglandin E(2) concentration was determined with an enzyme immunoassay. In addition, crystal attachment was evaluated with a liquid scintillation counter using [(14)C] calcium oxalate monohydrate crystals, and immunohistochemistry and an enzyme immunoassay were used to analyze and quantify the expression of hyaluronan, a crystal-binding molecule.

RESULTS

Cyclooxygenase 2-overexpressing Madin-Darby canine kidney cells produced about 10-fold more prostaglandin E(2) than wild-type Madin-Darby canine kidney cells, and their hyaluronan production was also upregulated. The attachment of calcium oxalate monohydrate crystals to cyclooxygenase 2-overexpressing Madin-Darby canine kidney cells was significantly reduced compared with their attachment to wild-type and mock-transfected Madin-Darby canine kidney cells. Pre-incubation of the cyclooxygenase 2-overexpressing cells, as well as the mock-transfected and wild-type cells with the cyclooxygenase 2 selective inhibitor etodolac, increased the cellular attachment of calcium oxalate monohydrate crystals in a dose-dependent manner.

CONCLUSIONS

These findings suggest that cyclooxygenase 2 expression and the resultant increase in endogenous prostaglandin E(2), leading to increased hyaluronan production, help to prevent nephrocalcinosis by inhibiting the attachment of calcium oxalate monohydrate crystals to the surface of renal epithelial cells.

Arjunolic acid: beneficial role in type 1 diabetes and its associated organ pathophysiology

In this review article, we describe the most recent development of the beneficial effect of arjunolic acid (AA) in reducing type 1 diabetic pathophysiology. Diabetic mellitus is a serious and growing health problem worldwide. Increasing evidence suggest that oxidative stress plays a pivotal role in the pathogenesis of diabetes and its associated complications. Use of antioxidant supplements as a complimentary therapeutic approach in diabetes has, therefore, been seriously considered worldwide. AA, a natural pentacyclic triterpenoid saponin, is well known for various biological functions including antioxidant activity. It could prevent the increased production of ROS, RNS, AGEs, and the 8OHdG/2dG ratio and increase the intracellular antioxidant defence system. Signal transduction studies showed that AA could prevent hyperglycaemia induced activation of MAPKs, PKC, NF-κB signalling cascades and apoptotic cell death. Combining, AA supplements could be regarded as beneficial therapeutics in the treatment of diabetes and its associated complications.

Early protective effect of mitofusion 2 overexpression in STZ-induced diabetic rat kidney

Diabetic nephropathy (DN) is a serious complication of diabetes with a poorly defined etiology and limited treatment options. Early intervention is key to preventing the progression of DN. Mitofusin 2 (Mfn2) regulates mitochondrial morphology and signaling, and is involved in the pathogenesis of numerous diseases. Furthermore, Mfn2 is also closely associated with the development of diabetes, but its functional roles in the diabetic kidney remain unknown. This study investigated the effect of Mfn2 at an early stage of DN. Mfn2 was overexpressed by adenovirus-mediated gene transfer in streptozotocin-induced diabetic rats. Clinical parameters (proteinuria, albumin/creatinine ratio), pathological changes, ultra-microstructural changes in nephrons, expression of collagen IV and phosph-p38, ROS production, mitochondrial function, and apoptosis were evaluated and compared with diabetic rats expressing control levels of Mfn2. Endogenous Mfn2 expression decreased with time in DN. Compared to the blank transfection control group, overexpression of Mfn2 decreased kidney weight relative to body weight, reduced proteinuria and ACR, and improved pathological changes typical of the diabetic kidney, like enlargement of glomeruli, accumulation of ECM, and thickening of the basement membrane. In addition, Mfn2 overexpression inhibited activation of p38, and the accumulation of ROS; prevented mitochondrial dysfunction; and reduced the synthesis of collagen IV, but did not affect apoptosis of kidney cells. This study demonstrates that Mfn2 overexpression can attenuate pathological changes in the kidneys of diabetic rats. Further studies are needed to clarify the underlying mechanism of this protective function. Mfn2 might be a potential therapeutic target for the treatment of early stage DN.

Is oxidative stress, a link between nephrolithiasis and obesity, hypertension, diabetes, chronic kidney disease, metabolic syndrome?

Epidemiological studies have provided the evidence for association between nephrolithiasis and a number of cardiovascular diseases including hypertension, diabetes, chronic kidney disease, metabolic syndrome. Many of the co-morbidities may not only lead to stone disease but also be triggered by it. Nephrolithiasis is a risk factor for development of hypertension and have higher prevalence of diabetes mellitus and some hypertensive and diabetic patients are at greater risk for stone formation. An analysis of the association between stone disease and other simultaneously appearing disorders, as well as factors involved in their pathogenesis, may provide an insight into stone formation and improved therapies for stone recurrence and prevention. It is our hypothesis that association between stone formation and development of co-morbidities is a result of certain common pathological features. Review of the recent literature indicates that production of reactive oxygen species (ROS) and development of oxidative stress (OS) may be such a common pathway. OS is a common feature of all cardiovascular diseases (CVD) including hypertension, diabetes mellitus, atherosclerosis and myocardial infarct. There is increasing evidence that ROS are also produced during idiopathic calcium oxalate (CaOx) nephrolithiasis. Both tissue culture and animal model studies demonstrate that ROS are produced during interaction between CaOx/calcium phosphate (CaP) crystals and renal epithelial cells. Clinical studies have also provided evidence for the development of oxidative stress in the kidneys of stone forming patients. Renal disorders which lead to OS appear to be a continuum. Stress produced by one disorder may trigger the other under the right circumstances.

Effects of pomegranate juice on hyperoxaluria-induced oxidative stress in the rat kidneys

To evaluate the role of the inducible nitric oxide synthase (iNOS), selective nuclear factor-kB (NF-kB), and p38-mitogene-activated protein kinase (p38-MAPK) on hyperoxaluria-induced oxidative stress and stone formation in rat kidneys. The rats were divided into five groups: group 1, control group; group 2: ethylene glycol (EG) group; group 3: EG + pomegranate juice (PJ)-low group; group 4: EG + PJ-middle group; group 5: EG + PJ-high group. Rats were sacrificed on 7, 15, and 45 days. The iNOS expression, p65-NF-kB and p38-MAPK activity, and oxidative stress markers were evaluated in the kidney. Crystal depositions were evident on day 7, and mild and severe crystallization were observed on day 15 and 45 in EG group, respectively. There was limited or no crystal formation in rats in both middle- and high-dose PJ groups when compared to low-dose PJ group. Crystal depositions, iNOS, p38-MAPK and p65-NF-kB activity, and oxidative stress markers were found to be decreased by middle- and high-dose PJ treatment. PJ was found to have inhibitory effects on renal tubular cell injury and oxidative stress caused by oxalate crystals by reducing ROS, iNOS, p38-MAPK, and NF-kB expression.

Prophylactic role of arjunolic acid in response to streptozotocin mediated diabetic renal injury: activation of polyol pathway and oxidative stress responsive signaling cascades

Diabetic nephropathy is a common cause for end-stage renal disease. Present study investigated the beneficial role of arjunolic acid (AA) against streptozotocin (STZ) induced diabetic nephropathy in rats. Diabetic renal injury was associated with increased kidney weight to body weight ratio, glomerular area and volume, blood glucose (hyperglycemia), urea nitrogen and serum creatinine. This nephro pathophysiology increased the productions of reactive oxygen species (ROS) and reactive nitrogen species (RNS), enhanced lipid peroxidation, protein carbonylation and decreased intracellular antioxidant defense in the kidney tissue. In addition, hyperglycemia activates polyol pathway by increasing aldose reductase (AR) with a concomitant reduction in Na+-K+-ATPase activity. Investigating the oxidative stress responsive signaling cascades, we found the activation of PKCdelta, PKCvarepsilon, MAPKs and NF-kappaB (p65) in the renal tissue of the diabetic animals. Furthermore, hyperglycemia disturbed the equilibrium between the pro and anti-apoptotic members of Bcl-2 family of proteins as well as reduced mitochondrial membrane potential, elevated the concentration of cytosolic cytochrome C and caspase-3 activity. Treatment of AA effectively ameliorated diabetic renal dysfunctions by reducing oxidative as well as nitrosative stress and deactivating the polyol pathways. Histological studies also support the experimental findings. Results suggest that AA might act as a beneficial agent against the renal dysfunctions developed in STZ-induced diabetes.

Differential effects of valproic acid on growth, proliferation and metastasis in HTB5 and HTB9 bladder cancer cell lines

High grade invasive bladder cancer is a leading cause of cancer deaths and treatment options are limited for this type of cancer. Recent studies have reported anticancer effects of valproic acid in many cancers and also in superficial bladder cancer. Acute valproic acid administration suppressed cell proliferation in a time- and dose-dependent manner in two muscle-invasive human bladder cancer cell lines (HTB5 and HTB9), with accompanying G1 phase cell cycle arrest. A significant decrease in colony formation ability and invasiveness was seen with valproic acid treatment though the effectiveness varied with cell type. Our results suggest a role for valproic acid in inhibiting growth and invasion of muscle-invasive bladder cancer.

Superoxide from NADPH oxidase as second messenger for the expression of osteopontin and monocyte chemoattractant protein-1 in renal epithelial cells exposed to calcium oxalate crystals

OBJECTIVE To test the hypothesis that exposure of a renal epithelial cell line, NRK52E, to calcium oxalate monohydrate crystals (COM) would up-regulate NADPH oxidase subunit p47(phox), enhance superoxide production and increase monocyte chemoattractant protein-1 (MCP-1) and osteopontin mRNA levels. MATERIALS AND METHODS Confluent cultures of NRK52E cells were exposed to COM (66.7 microg/cm(2)) with or with no pretreatment with diphenileneiodium chloride (DPI, 10 x 10(-6)m) an inhibitor for NADPH oxidase, under serum-free conditions. The conditioned medium was collected and total cellular RNA isolated from the cells, and subjected to enzyme-linked immunosorbent assay and real-time polymerase chain reaction (PCR). Production of reactive oxygen species (ROS) was estimated by dihydroethidium (DHE) staining using a fluorescence microscope. Immunohistochemistry and real-time PCR were used to analyse p47(phox) in NRK52E cells. RESULTS In COM treated NRK52E cells there was enhanced expression of p47(phox) and production of superoxide. COM-induced production of MCP-1 and osteopontin was significantly reduced after treatment with DPI. CONCLUSIONS While the generation of a lot of ROS might play a major role in tissue injury or death, the regulated generation of low concentration of ROS, possibly by NADPH oxidase, may represent a second messenger system for generation of COM-induced MCP-1 and osteopontin production in the renal tubules.

NF-kappaB activation in renal tubular epithelial cells by oxalate stimulation

OBJECTIVES

The transcription factor nuclear factor-kappaB (NF-kappaB) is involved in inflammatory and immune responses through the induction of various cytokines and growth factors. Recently, the coordinated action of NF-kappaB and activator protein-1 was reported in osteopontin (OPN) expression. In the present study, we demonstrated that oxalate induces OPN expression by activating NF-kappaB in renal tubular cells. Furthermore, we investigated the inhibitory effect of N-acetyl-L-cysteine (NAC) on NF-kappaB activation in the human renal tubular cell line.

METHODS

All of the experiments were carried out using human kidney-2 cells, which are human proximal tubular epithelial cells immortalized by transduction with the human papillomavirus 16E6/E7 gene. The time-dependent extraction of total protein was performed after the uptake of 0.5 mM oxalate by the cells. The NF-kappaB activation and OPN expression were examined by western blotting and immunocytochemistry.

RESULTS

As a result of oxalate stimulation, the amount of p65 subunit in the nucleus increased significantly (P < 0.05), and NAC significantly inhibited the translocation of p65 into the nucleus (P < 0.05).

CONCLUSION

These observations indicate that NAC can be used as a drug to prevent stone formation.

Role of mitochondrial dysfunction in cellular responses to S-(1,2-dichlorovinyl)-L-cysteine in primary cultures of human proximal tubular cells

The nephrotoxic metabolite of the environmental contaminant trichloroethylene, S-(1,2-dichlorovinyl)-l-cysteine (DCVC), is known to elicit cytotoxicity in rat and human proximal tubular (rPT and hPT, respectively) cells that involves inhibition of mitochondrial function. DCVC produces a range of cytotoxic and compensatory responses in hPT cells, depending on dose and exposure time, including necrosis, apoptosis, repair, and enhanced cell proliferation. The present study tested the hypothesis that induction of mitochondrial dysfunction is an obligatory step in the cytotoxicity caused by DCVC in primary cultures of hPT cells. DCVC-induced necrosis was primarily a high concentration (> or =50 microM) and late (> or =24h) response whereas apoptosis and increased proliferation occurred at relatively low concentrations (<50 microM) and early time points (< or =24h). Decreases in cellular DNA content, indicative of cell loss, were observed at DCVC concentrations as low as 1 microM. Involvement of mitochondrial dysfunction in DCVC-induced cytotoxicity was supported by showing that DCVC caused modest depletion of cellular ATP, inhibition of respiration, and activation of caspase-3/7. Cyclosporin A protected cells against DCVC-induced apoptosis and both cyclosporin A and ruthenium red protected cells against DCVC-induced loss of mitochondrial membrane potential. DCVC caused little or no activation of caspase-8 and did not significantly induce expression of Fas receptor, consistent with apoptosis occurring only by the mitochondrial pathway. These results support the conclusion that mitochondrial dysfunction is an early and obligatory step in DCVC-induced cytotoxicity in hPT cells.

Apatite induced renal epithelial injury: insight into the pathogenesis of kidney stones

PURPOSE

Kidney stone formation is associated with the deposition of hydroxyapatite as subepithelial plaques or tubular deposits in the renal papillae. We investigated the effect of renal epithelial exposure to hydroxyapatite crystals in vitro to develop an insight into the pathogenesis of kidney stones.

MATERIALS AND METHODS

NRK52E cells (No. CRL-1571, ATCC) were exposed to 67 or 133 microg/cm(2) hydroxyapatite (No. 21223, Sigma-Aldrich) or calcium oxalate monohydrate crystals (No. 27609, BDH Industries, Poole, United Kingdom). In some studies cells were also exposed to crystals from the basal side. After 3 or 6 hours of exposure medium was analyzed for lactate dehydrogenase, 8-isoprostane and H(2)O(2). Medium collected after cell exposure on the apical side was also analyzed for the production of monocyte chemoattractant protein-1 and prostaglandin E2. Cells were stained with DAPI to determine apoptotic activity and examined by scanning electron microscopy to observe crystal-cell interaction.

RESULTS

Cell exposure to hydroxyapatite resulted in H(2)O(2) and 8-isoprostane production as well as in lactate dehydrogenase release. Apical exposure appeared more provocative and injurious than basal exposure. Exposure to hydroxyapatite for 6 hours resulted in increased apoptotic activity. Apical exposure also resulted in increased monocyte chemoattractant protein-1 and prostaglandin E2 production.

CONCLUSIONS

Cell exposure to hydroxyapatite crystals induced oxidative stress and lipid peroxidation. It caused up-regulation of the inflammation mediators that may be responsible for the kidney inflammation in patients with stones that is associated with tubular hydroxyapatite deposition. It may also have a role in the eruption of subepithelial Randall's plaques to the papillary surface.

Oxalate exposure provokes HSP 70 response in LLC-PK1 cells, a line of renal epithelial cells: protective role of HSP 70 against oxalate toxicity

We investigated the effects of oxalate on immediate early genes (IEGs) and stress protein HSP 70, commonly induced genes in response to a variety of stresses. LLC-PK1 cells were exposed to oxalate. Gene transcription and translation were monitored by Northern and Western blot analysis. RNA and DNA synthesis were assessed by [(3)H]-uridine and [(3)H]-thymidine incorporation, respectively. Oxalate exposure selectively increased the levels of mRNA encoding IEGs c-myc and c-jun as well as stress protein HSP 70. While expression of c-myc and c-jun was rapid (within 15 min to 2 h) and transient, HSP 70 expression was delayed (approximately 8 h) and stable. Furthermore, oxalate exposure resulted in delayed induction of generalized transcription by 18 h and reinitiation of the DNA synthesis by 24 h of oxalate exposure. Moreover, we show that prior induction of HSP 70 by mild hypertonic exposure protected the cells from oxalate toxicity. To the best of our knowledge this is the first study to demonstrate rapid IEG response and delayed heat-shock response to oxalate toxicity and protective role of HSP 70 against oxalate toxicity to renal epithelial cells. Oxalate, a metabolic end product, induces IEGs c-myc and c-jun and a delayed HSP 70 expression; While IEG expression may regulate additional genetic responses to oxalate, increased HSP 70 expression would serve an early protective role during oxalate stress.

Naturally produced crystals obtained from kidney stones are less injurious to renal tubular epithelial cells than synthetic crystals

OBJECTIVE

To determine the differences in cell responses to synthetic and biological crystals of calcium oxalate (CaOx) and brushite

MATERIALS AND METHODS

Nephrolithiasis depends on crystal retention within the kidneys, often promoted by crystal attachment to the injured renal epithelium; studies often use various crystals that might be injurious to cells and cause the exposure of crystal binding molecules on cell surfaces, thus promoting crystal attachment and retention. The synthetic crystals used in these studies might be more injurious than the biological crystals naturally produced in the kidneys and that form kidney stones. We exposed the renal epithelial cell line NRK 52E in vitro to CaOx or brushite crystals at 67 or 133 microg/cm(2) for 3 or 6 h. Synthetic crystals were purchased and the biocrystals were obtained by pulverizing CaOx and brushite stones. We determined the release of lactate dehydrogenase (LDH), hydrogen peroxide (H(2)O(2)) and 8-isoprostane (8-IP), and monocyte chemoattractant protein-1 (MCP-1), as markers of injury, oxidative stress and inflammation, respectively. Cells were also examined after trypan blue staining to determine their membrane integrity. We also examined crystals of CaOx by scanning electron microscopy both in the native state as well as after decalcification.

RESULTS

Exposure to both the synthetic and biological crystals resulted in a significant increase in LDH release and trypan blue staining, as a sign of crystal-induced injury. There was increased production of H(2)O(2) and 8-IP, suggesting the development of oxidative stress. In addition MCP-1 production was also significantly increased. However, the synthetic crystals caused significantly higher increases in all the indicators than the biological crystals.

CONCLUSIONS

These results indicate that even though both synthetic and naturally produced biocrystals invoke a response from the renal epithelial cells, the latter are significantly less injurious and inflammatory. Exposure to low concentrations of these crystals alone might not invoke an inflammatory response, cause the uncovering of crystal binding molecules on epithelial cell surfaces, and promote crystal attachment and retention.

Continuous infusion of oxalate by minipumps induces calcium oxalate nephrocalcinosis

It is hypothesized that oxalate plays an active role in calcium oxalate (CaOx) nephrocalcinosis and oxalate driven nephrolithiasis by interacting with the kidney. We developed an adjustable, nonprecursor, continuous infusion model of hyperoxaluria and CaOx nephrocalcinosis to investigate this hypothesis. Minipumps containing PBS or KOx (60-360 micromol/day; n = 5-7/dose) were implanted subcutaneously in male Sprague-Dawley rats on D0 and D6. Rats were killed on D13. Oxalate excretion and CaOx crystalluria were monitored by 20+4 h urine collections. Localization and content of intrarenal crystals were determined on frozen sections using polarization and microFTIR. Oxalate excretion was significantly elevated in all KOx rats (P < or = 0.005). CaOx crystalluria was most persistent in the 240-360 micromol/day KOx rats, but even 60 micromol/day KOx rats showed sporadic crystalluria. One hundred percent of KOx rats had CaOx nephrocalcinosis as confirmed by microFTIR. Most crystals were localized to the lumens of the corticomedullary collecting ducts. A few crystals are localized just under the papillar urothelium. The minipump model is the first model of hyperoxaluria to provide continuous infusion of oxalate. It permits control of the levels of hyperoxaluria, crystalluria and CaOx nephrocalcinosis. The level of sustained hyperoxaluria and CaOx nephrocalcinosis induced by treatment with 360 micromol/day KOx for 13D models the conditions frequently observed in jejunoileal bypass patients. Adjustments in the length of treatment and level of hyperoxaluria may allow this model to also be used to study the oxalate driven CaOx-nephrolithiasis common in patients with hyperoxaluria due to other causes.

Oxalate is toxic to renal tubular cells only at supraphysiologic concentrations

BACKGROUND

Oxalate-induced tissue damage may play an initiating role in the pathophysiology of calcium oxalate nephrolithiasis. The concentration of oxalate is higher in the renal collecting ducts ( approximately 0.1 to 0.5 mmol/L) than in the proximal tubule ( approximately 0.002 to 0.1 mmol/L). In the present investigation, we studied the damaging effect of oxalate to renal proximal and collecting tubule cells in culture.

METHODS

Studies were performed with the renal proximal tubular cell lines, LLC-PK1 and Madin Darby canine kidney II (MDCK-II), and the renal collecting duct cell lines, rat renal cortical collecting duct (RCCD1) and MDCK-I. Confluent monolayers cultured on permeable growth substrates in a two-compartment culture system were apically exposed for 24 hours to relatively low (0.2, 0.5, and 1.0 mmol/L) and high (5 and 10 mmol/L) oxalate concentrations, after which several cellular responses were studied, including monolayer morphology (confocal microscopy), transepithelial electrical resistances (TER), prostaglandin E(2) (PGE(2)) secretion, lactate dehydrogenase (LDH) release, DNA synthesis ([(3)H]-thymidine incorporation), total cell numbers, reactive oxygen species (H(2)O(2)) generation, apoptotic (annexin V and DNA fragmentation), and necrotic (propidium iodide influx) cell death.

RESULTS

Visible morphologic alterations were observed only at high oxalate concentrations. TER was concentration-dependently decreased by high, but not by low, oxalate. Elevated levels of PGE(2), LDH, and H(2)O(2) were measured in both cell types after exposure to high, but not to low oxalate. Exposure to high oxalate resulted in elevated levels of DNA synthesis with decreasing total cell numbers. High, but not low, oxalate induced necrotic cell death without signs of programmed cell death.

CONCLUSION

This study shows that oxalate is toxic to renal tubular cells, but only at supraphysiologic concentrations.

Hyperoxaluria-induced oxidative stress and antioxidants for renal protection

Renal cellular exposure to oxalate (Ox) and/or CaOx crystals leads to the production of reactive oxygen species (ROS), development of oxidative stress followed by injury and inflammation. Renal injury and inflammation appear to play a significant role in stone formation. ROS are produced from many sources and involve a variety of signaling pathways. Tissue culture and animal model studies show that treatments with anti-oxidants and free radical scavengers reduce Ox/CaOx crystal induced injuries. In addition, CaOx crystal deposition in kidneys is significantly reduced by treatments with antioxidants and free radical scavengers, indicating their efficacy. These results point towards a great potential for the therapeutic application of antioxidants and free radical scavengers to reduce stone recurrence particularly after shock wave lithotripsy, which is itself known to generate ROS and cause renal damage.

Oxalate stimulates IL-6 production in HK-2 cells, a line of human renal proximal tubular epithelial cells

BACKGROUND

Oxalate is a metabolic end product excreted primarily by the kidney and associated with several pathologic conditions. The most common pathologic condition involving oxalate is the formation of calcium oxalate stones in the kidney. Several stimuli have been implicated in the development of glomerular and tubular injury in various forms of immune-mediated renal diseases. The elevated level of interleukin-6 (IL-6) has been reported in the urine of kidney stone-forming patients. In the present study, we investigated the role of oxalate, a major constituent of calcium oxalate kidney stone disease, in the production of IL-6 in normal human HK-2 kidney cells.

METHODS

Confluent cultures of HK-2 cells (a renal epithelial cell line of human origin) were exposed to various concentrations of oxalate (0.2 to 2.0 mmol/L) and lipopolysaccharide (LPS) (0.1 and 10 mug/mL) for various time points (4-24 h) under serum-free conditions. The conditioned mediums were collected, and an IL-6 protein level was measured by enzyme-linked immunosorbent assay (ELISA). The total cellular RNA was isolated from the cells and subjected to relative quantitative reverse transcription-polymerase chain reaction (RT-PCR) to determine the expression of IL-6 mRNA. The statistical analysis of the results was carried out using the Student t test.

RESULTS

HK-2 cells express IL-6 mRNA and protein. Oxalate increased the secretion of IL-6 protein in HK-2 cells in a concentration-dependent fashion. Oxalate exposure to HK-2 cells also induced transcriptional up-regulation of the IL-6 gene, as determined by the increased level of IL-6 mRNA expression following treatment with oxalate. Moreover, the effects of oxalate on IL-6 expression were time- and concentration-dependent. This is the first report demonstrating the regulation of IL-6 by oxalate.

CONCLUSION

This study provides the first direct evidence that oxalate up-regulates the expression and secretion of IL-6 in renal epithelial cells. The increased IL-6 expression and secretion by renal epithelial cells may play a critical role in the progression of urolithiasis in hyperoxaluric conditions.

JNK/SAPK and p38 SAPK-2 mediate mechanical stretch-induced apoptosis via caspase-3 and -9 in NRK-52E renal epithelial cells

BACKGROUND/AIMS

In renal epithelial cells, mechanical forces produced from urinary obstruction serve as potential mediators of apoptosis by activating specific intracellular signaling pathways. In this study, we sought to further define the role of JNK and p38 SAPK-2 pathway and caspase activation in stretch-induced apoptosis.

METHODS

Immortalized cell lines derived from the various components of the nephron were subjected to cyclical stretch and their differential apoptotic response was assessed. Pharmacologic inhibitors and Western blot analysis were used to assess the involvement of the MAPK pathways. Caspases' activity was assessed with ELISA and by Western blot analysis.

RESULTS

Stretch-induced apoptosis was dependent upon the cell phenotype and the degree of stretch. In NRK-52E cells, it was mediated through both JNK and p38 SAPK-2 pathways, and inhibition of either pathway reduced the degree of stretch-induced apoptosis. Stretched cells showed increased activity of caspase-3 and -9 but not -2 or -8. Stretch-induced apoptosis was modulated by inhibition of caspase-3 and to a lesser extent by caspase-9.

CONCLUSION

These findings suggest that stretch induces apoptosis in renal epithelial cells through the specific activation of JNK/SAPK and p38 SAPK-2 pathways and is dependent on the activation of caspase-3 and -9.

OXALATE TOXICITY IN CULTURED MOUSE INNER MEDULLARY COLLECTING DUCT CELLS

PURPOSE

Oxalate, a metabolic end product and a major constituent of the majority of renal stones, has been shown to be toxic to renal epithelial cells of cortical origin. However, to our knowledge it is unknown whether inner medullary collecting duct (IMCD) cells, which are physiologically exposed to higher concentrations of oxalate, also behave in a similar manner.

MATERIALS AND METHODS

A line of IMCD cells was exposed to oxalate (0.2 to 10 mM) for various time points. Trypan blue, and hematoxylin and eosin stains were used to assess cell morphology and membrane integrity. The production of reactive oxidative species was determined using the nitro blue tetrazolium reaction and crystal violet staining was used to measure cell density.

RESULTS

Exposure of IMCD cells to oxalate produced time and concentration dependent changes in the light microscopic appearance of the cells. Long-term exposure to oxalate resulted in alterations in cell viability with net cell loss following exposure to concentrations of 2 mM and greater. Free radical production was time and concentration dependent. Crystal formation occurred in less than 1 hour and cells in proximity to crystals lost membrane integrity. Compared to IMCD cells LLC-PK1 and HK2 cells showed significant toxicity starting at lower oxalate concentrations (0.4 mM and above).

CONCLUSIONS

To our knowledge the results provide the first direct demonstration of toxic effects of oxalate in IMCD cells, a line of renal epithelial cells of the inner medullary collecting duct, and suggest that cells lining the collecting duct are relatively resistant to oxalate toxicity.

Cellular and molecular gateways to urolithiasis: a new insight

Urolithiasis is a relevant clinical problem in everyday practice with a subsequent burden for the health system. Urolithiasis is classically explained as the derangement in the process of biomineralization involving the equilibrium between promoters and inhibitors of crystallization: a deficit of one or several inhibitors or an excess of one or several promoters plays a pivotal role in the stone formation. The revolutionary introduction of the molecular biology in medicine has given a new insight in urolithiasis too. Genetic factors have also been postulated to play an important role. A review of the current knowledge on urolithiasis based upon a molecular and genetic approach is reported.

Effects of oxalate on IMCD cells: a line of mouse inner medullary collecting duct cells

Oxalate, a metabolic end product and a major constituent of the majority of renal stones, has been shown to be toxic to renal epithelial cells of cortical origin. However, it is unknown whether inner medullary collecting duct (IMCD) cells that are physiologically exposed to higher concentrations of oxalate also behave in a similar manner. In the present study, we examined the effects of oxalate on IMCD cells. IMCD cells from the mouse were maintained in DMEM/F12 media supplemented with fetal bovine serum and antibiotics. Exposure of IMCD cells to oxalate produced time- and concentration-dependent changes in the light microscopic appearance of the cells. Long-term exposure to oxalate resulted in alterations in cell viability, with net cell loss after exposure to concentrations of 2 mM or greater. The production of free radicals was directly related to the exposure time and the concentration of oxalate. Crystal formation occurred in less than 1 h and cells in proximity to crystals would lose membrane integrity. Compared with IMCD cells, LLC-PK1 cells as well as HK-2 cells showed significant toxicity starting at lower oxalate concentrations (0.4 mM or greater). These results provide the first direct demonstration of toxic effects of oxalate in IMCD cells, a line of renal epithelial cells of the inner medullary collecting duct, and suggest that the cells lining the collecting duct are relatively resistant to oxalate toxicity.

Gut-inhabiting bacterium Oxalobacter formigenes: role in calcium oxalate urolithiasis

Oxalate plays a crucial role in the formation of most renal stones. Oxalate is a common constituent of most diets and a byproduct of metabolism, and if it is not sufficiently degraded, it may accumulate. In humans, gut bacteria degrade 70 to 100 mg of oxalate per day. Oxalobacter formigenes is a gram-negative, obligately anaerobic, rod-shaped bacterium with an absolute requirement for oxalate. Although not present in the gut at birth, it quickly colonizes most children, and there is epidemiologic evidence that its absence is a risk factor in calcium oxalate stone formation. We review the metabolism, genetics, and identification of this organism and its possible therapeutic role in recurrent stone-forming patients.

Role of p38 MAP kinase signal transduction in apoptosis and survival of renal epithelial cells

The p38 MAP kinase signal transduction pathway is activated by various forms of cellular stress. While, in many tissues, activation of p38 MAP kinase is associated with apoptosis, in some tissues p38 activation is critical for survival. Oxalate deposits are associated with several pathological conditions that involve aberrant proliferation and cellular apoptosis. Studies from our laboratory demonstrated that exposure of renal epithelial cells to oxalate and COM-crystals resulted in activation of the p38 MAP kinase pathway. Moreover, the inhibition of the p38 MAO kinase pathway resulted in the inhibition of oxalate as well as COM-crystal-induced reinitiation of the DNA synthesis. These results suggest a critical role for the p38 MAP kinase pathway in pathological conditions associated with cellular proliferation and apoptosis following deposition of calcium oxalate.

COM crystals activate the p38 mitogen-activated protein kinase signal transduction pathway in renal epithelial cells

Interaction of calcium oxalate monohydrate (COM) crystals with renal cells has been shown to result in altered gene expression, DNA synthesis, and cell death. In the current study the role of a stress-specific p38 MAP kinase-signaling pathway in mediating these effects of COM crystals was investigated. Exposure of cells to COM crystals (20 microg/cm(2)) rapidly stimulated strong phosphorylation and activation of p38 mitogen-activated protein kinase (p38 MAP kinase) and re-initiation of DNA synthesis. Inhibition of COM crystal binding to the cells by heparin blocked the effects of COM crystals on p38 MAPK activation. We also show that specific inhibition of p38 MAPK by 4-(4-fluorophenyl)-2-(4-methylsulfonylphenyl)-5-(4-pyridyl) imidazole (SB203580) or by overexpression of a dominant negative mutant of p38 MAP kinase abolishes COM crystal-induced re-initiation of DNA synthesis. The inhibition is dose-dependent and correlates with in situ activity of native p38 MAP kinase, determined as mitogen-activated protein kinase-activated protein kinase-2 (MAPKAP kinase-2) activity in cell extracts. In summary, inhibiting activation of p38 MAPK pathway abrogated the DNA synthesis in response to COM crystals. These data are the first demonstrations of activation of the p38 MAPK signaling pathway by COM crystals and suggest that, in response to COM crystals, this pathway transduces critical signals governing the re-initiation of DNA synthesis in renal epithelial cells.

Pharmacologically activated migration of aortic endothelial cells is mediated through p38 SAPK

Impairment in endothelial cell (EC) function plays a central role in vascular diseases (e.g. atherosclerosis, restenosis, diabetic angiopathies, microvascular angina, peripheral arterial disease). BRX-235 (a novel small molecule synthesized by Biorex, Hungary) has a potent vasculoprotective activity in different in vivo and in vitro studies. Since the importance of the p38 pathway in EC homeostasis and migration in particular is well documented, we have carried out studies to address the role of the p38 stress activated protein kinase (p38 SAPK) in the mode of action of BRX-235. In this study, Bovine aortic endothelial cells were used in a wounding migration assay (WMA) and for Western-blot analysis to study the effect and molecular mechanism of BRX-235-induced EC migration. The bovine aortic endothelial (BAE) cells were shown to be good models for EC migration. Both endothelial cell growth factor (ECGF)- and BRX-235-induced BAE cell migration were shown to be inhibited by SB 203580, a specific inhibitor of p38 SAPK. It was also shown that, BRX-235 induces phosphorylation of p38 SAPK without affecting p38 SAPK protein levels. Thus, BRX-235 acts upstream of p38 SAPK. In summary, we have shown that p38 SAPK is a potential pharmacological mediator for candidate drugs that target the endothelium.